1. Field of the Invention
The present invention relates to lumber. More particularly, the present invention relates to processes and apparatuses for cutting logs into boards.
2. Description of the Prior Art
In the lumber industry, logs are typically processed by longitudinal straight cutting, first to form a cant, and then to produce boards. Since trees grow radially, straight cutting sacrifices fiber yield in the final board product. Further, the presence of defects, such as knots is disadvantageous since a single knot will appear in all boards cut through it. Unless the cut is exactly tangential to the knot, the deleterious effect of these defects is magnified since the surface area and volume of each knot occupies a greater portion of the board, thereby requiring complete rejection or at least down-grading the lumber produced. When logs used are from old growth or trees of otherwise exceptional quality, the board yield from straight cutting is acceptable because the concentration of defects is naturally, or by definition low. However, diminishing supply of such trees, and the heavy environmental implications of over-harvesting old growth has created a need for producing wooden boards from logs with a higher concentration of defects and/or from less environmentally damaging new growth trees.
Continuous band saws which are supported and driven by rollers in a housing have been used in cutting boards from logs. The cutting area is invariably a straight edge in saws so used, despite the disadvantages of straight cutting, described above. Further, the lumber industry uses thick saw blades with wide kerfs, requiring large horsepower electric motors to drive the saws. This is due to extreme tension placed on the saw in order to maintain saw travel, guide, and drive. Saw blades must accordingly be of a thickness to withstand such tension, having a lower limit of 1/8" when high tensile materials are used.
Stephan, British Patent No. 17,372, describes a band saw for cutting sections of lumber, in which the saw moves along the length of the log, making a longitudinal cut. U.S. Pat. Nos. 340,964; 2,876,809; and 4,193,192 describe various saw blade drives and support rolls for a continuous band saw.
Moriya in UK Published Patent Application GB 2 221 187 A, and U.S. Pat. No. 4,458,567 to Tuomaala describe various shape and dimension detection techniques for maximizing the lumber output quantity and/or quality. Soviet Patent SU 1142276 A to the Mosc. Forestry Inst. describes the determination of a given sector of a log having the highest concentration of knots.
U.S. Pat. No. 1,732,743 to Dougherty describes a process for cutting logs in which the log is split into wedge cants, the core removed, and the cants are further cut into boards. U.S. Pat. No. 4,895,197 to Andersen describes a method and apparatus for sawing logs with a trio of straight circular saws. U.S. Pat. No. 4,930,556 to Prihoda describes a method for pealing a log for veneers, in which a straight blade is applied along the full length of the log, and a spiral cut through growth curves is made.
The Maksimov patent, SU 632566 describes the use of electromagnetic induction to stabilize a flexible steel tape blade. Soviet Patents 489632 and 579140 describe the use of magnets to secure continuous band saws onto associated rollers and/or other guide means. An apparatus in which a band saw blade is held in a curve for sharpening purposes is described by Swiss Patent No. 116,338, to Eisermann et al. U.S. Pat. No. 5,291,927 to Gonner describes a device for straightening wooden boards by applying opposite pressure.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.